As is known, a so-called “Holter” monitor allows ambulatory EKG measurement of a patient. A Holter monitor generates an electrocardiogram (EKG) recording over a period of 24 or more hours. Three electrodes are attached to the patient's chest and connected to a small portable EKG recorder by lead wires. When operating, the patient goes about his or her usual daily activities (except for activities such as taking a shower, swimming, or any activity causing an excessive amount of sweating which would cause the electrodes to become loose or fall off).
There are two conventional types of Holter monitoring. For continuous recording, the EKG is recorded continuously during the entire testing period. For event monitoring, or loop recording, the EKG is recorded only when the patient starts the recording, i.e., when symptoms are felt. The patient starts the event monitoring by pushing a button or the like.
Holter monitoring may be done when a heart arrhythmia is suspected but not seen on a resting or signal-average EKG, since arrhythmias may be transient or intermittent and may not be seen during the shorter recording times of the resting or signal-average EKG.
While the Holter monitor allows an EKG trace to be generated in an ambulatory environment, e.g., during usual daily activities, the EKG is only useful to diagnose certain medical conditions. A variety of other medical conditions may also be intermittent in nature. For example, a dizzy spell, or hot flashes can occur intermittently. The Holter monitor, which provides an EKG, is not well suited to detect and to characterize these or some other types of intermittent medical conditions. For these, different ambulatory monitors are more appropriate.
Apparatus and techniques are known which transmit light into a patient and receive resulting light from the patient. One such apparatus, a pulse oximeter, transmits light into a finger of a patient and uses the resulting received light to determine a blood oxygenation level of the patient. Other, more complex systems under exploration and development, use multiple light sources and multiple light receivers to detect such medical conditions as hemorrhage and ischemia.
Existing apparatus, which generates light into and receives light from a patient, is known to be bulky and not suitable for ambulatory measurements. Some such apparatus requires that bulky light fibers be attached to the patient.